This application is based on and claims priority to Japanese Patent Application No. 11-341304, filed Nov. 30, 1999, the entire contents of which is hereby expressly incorporated by reference.
1 Field of the Invention
The present invention generally relates to idle speed controls for internal combustion engines used to power a watercraft. More specifically, the present invention relates to such systems in which throttle bypass levels are adjusted based upon the speed of the watercraft.
2 Related Art
Outboard motors are powered by engines contained within an engine compartment of the outboard motor. The outboard motors are conventionally attached to watercraft to power the watercraft in a forward or reverse direction. As is known, the engine of the outboard motor is subject to increased loading when compared to that of an automobile, for instance. This increased loading generally results from the nature of the outboard motor and the environment of use of the outboard motor.
The engines that power the outboard motors may contain an intake system featuring a bypass passage. The bypass passage typically is linked to the intake system upstream and downstream of a throttle control valve. As is known, the throttle control valve controls the amount of air flowing through the induction system into the engine for combustion. When the throttle control valve is closed, the air flow rate is minimized and when the throttle control valve is opened, the flow rate through the induction system can be somewhat controlled. The use of a bypass passage allows air to bypass the throttle control valve for supply to the engine even when the throttle control valve is closed. In some instances, an ISC, or idle speed control valve, is positioned along the bypass passage. The ISC valve can be used to fine tune the idling engine speed when the throttle control valve is in a closed position.
Conventional ISC valves are designed to open when the throttle valve suddenly closes following a period of high speed operation. It is thought that by opening the ISC valves when the throttle valve closes, misfiring and stalling can be obviated or greatly reduced. Generally speaking, the ISC valves are closed when the throttle valve is opened and when the engine speed is low. The ISC valves are opened when the throttle valve is closed and when the engine speed is high. In some applications, the ISC valves can be suddenly opened during high speed operation of the engine and then gradually closed after the engine speed decreases below a preset level.
The positioning of the idle speed control valve often is controlled by inexpensive step motors. The inexpensive step motors typically have a slow response characteristic. In other words, the command to move is followed by a slight delay before the movement occurs. In a conventional ISC valve control strategy, the ISC valve remains closed while the throttle valve is opening. The ISC valve remains in the closed position until the throttle angle is rapidly decreased (i.e., the throttle valve closes under the biasing force of a spring, such as when the opening force provided by an operator controlled actuator is removed). Once the throttle angle is rapidly decreased, the ISC valve slowly opens under the control of the stepper motor. Because of the slow opening rate of the idle speed control valve, the air flow through the induction system does not properly match the desired change of the engine speed resulting from the rapid change in a throttle opening position. Accordingly, the engine can stall or misfire due to an inadequate supply of intake air. One way of correcting this is to provide an idle speed control valve in which the ISC valve opens more rapidly for each input signal to the stepper motor. A drawback from this approach is that a large ISC valve is required and the larger ISC valves increase cost and weight.
Another solution to the misfiring and stalling of the engine is to make the ISC valve more accurately follow the changes in a throttle angle and consequently the engine speed. Preferably, this arrangement would result in the ISC valve being maintained in an open position while the throttle angle is open. This arrangement ensures that a more-than-adequate air supply is provided when the throttle angle is rapidly decreased. The ISC valve then can close with the throttle valve. It should be noted, however, that if the closing speed of the ISC valve is too rapid, the engine speed can overshoot and hunt. Closing the ISC valve too rapidly can also cause the engine speed to rapidly decrease, which can produce excessive loads within the engine and cause the engine to stall. On the other hand, if the closing speed of the ISC valve is too slow, the engine speed decreases too slowly. Moreover, when the transmission is in the forward drive position, the advancing force of the watercraft, which drives the propeller, can further slow the engine speed decrease. As a result, the watercraft is not as responsive to changes in operator demand. The slow decrease in engine speed also makes it difficult to shift gears, especially from a forward position to a neutral position.
Accordingly, an arrangement is desired such that, when throttle valve suddenly closes, the watercraft is sufficiently responsive to changes in the operators demand, the engine speed does not hunt and the engine does not stall.
Accordingly, an idle speed control system is desired in which an idle speed control valve is opened as a throttle valve is opened and in which the idle speed control valve is closed at different rates, which are dependent upon the speed of the watercraft, when the throttle valve is rapidly closed.
One aspect of the present invention involves an engine for a watercraft that includes a cylinder body and at least one cylinder bore being formed in the cylinder body. A piston is mounted for reciprocation within the cylinder bore. A cylinder head is disposed over a first end of the cylinder bore. A crankcase member is disposed over a second end of the cylinder bore and an output shaft is disposed at least partially within a crankcase chamber at least partially defined by the crankcase member. The output shaft powers an output device. A combustion chamber is defined at least partially within the cylinder bore between the cylinder head and the piston. An intake conduit communicates with the combustion chamber. A throttle valve is disposed within the intake conduit. A throttle valve sensor is capable of sensing a position of the throttle valve. A bypass passage communicates with the intake conduit at a location between the throttle valve and the combustion chamber. An idle speed control valve is disposed along the bypass passage. A speed sensor is capable of deducing a traveling speed of the watercraft. A controller is electrically communicating with the idle speed control valve, the speed sensor and the throttle valve sensor. The controller is adapted, when the throttle valve is rapidly closed, to close the idle speed control valve a first rate when the watercraft is traveling at a speed greater than a preset value and a second rate when the watercraft is traveling below the preset value.
Another aspect of the present invention involves a method of controlling the movement of an idle speed control valve. The method comprises detecting a throttle angle, sensing a position of the idle speed control valve, determining a target position of the idle speed control valve position, comparing the target position to the sensed position, sensing a speed of a watercraft, moving the idle speed control valve at a first rate if the target position and the sensed position differ and the speed of the watercraft is above a preset value and moving the idle speed control valve at a second rate if the target position and the sensed position differ and the speed of the watercraft is below the preset value.
A further aspect of the present invention involves a method of controlling an idle speed control valve in an engine for a watercraft. The method comprises sensing a throttle angle, sensing a traveling speed of the watercraft, moving the valve at a first rate if the traveling speed of the watercraft is above a preset value and moving the valve at a second rate if the traveling speed of the watercraft is below the preset value.